The sky appears blue,when viewed from Earth,because of the scattering of the light.scattering is the phenomenon by which a beam of light is redirected in many different directions when it interacts with a particle of matter.when sunlight strikes molecules in our atmosphere,the light is redirected in many directions.The blue light is scattered more than the red light causing the sky to be blue.In the space,there is no,light will not scatter in space.This is the cause of dark sky when viewed from space. 
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Visible light consists of seven colours. Among them red can travel a lot with out deviating. Because wavelength of it I maximum. But violet oon the other side of the spectrum gets deviated easily. Atmosphere of earth is filled with particles. These particles make the light spread or scatter. Violet and its component colours get easily spread. It is third what makes the sky blue. This is reflected by vast oceans and hence appear blue. there is no atmosphere in outer space because of the lack of these gravitational force to hold on the particles. Thus light wont be made to scatter. Absence of medium means absence of surface for light to fall on. This means absence of colour. Thus it will appear black